Remarkably enhanced dehydrogenation properties and mechanisms of MgH2 by sequential-doping of nickel and graphene

Abstract

Magnesium hydride MgH2 is an attractive hydrogen storage material because of its high volumetric and gravimetric densities, inexpensiveness and abundance. However, its high dehydrogenation temperature resulted from the unfavorable thermodynamic and kinetic barriers limits its practical applications. Herein, we first propose an efficient strategy for remarkably enhancing the dehydrogenation properties of MgH2 by sequential-doping of nickel (Ni) and graphene (G) via mechanical milling. This method can not only accelerate the refinement of MgH2 grains and particles, but also significantly decrease its dehydrogenation temperature relative to G single-doping and Ni/G simultaneous-doping systems. First-principles calculations indicate that the excellent dehydrogenation properties of Ni/G sequential-doped MgH2 system are closely associated with the dual effects involving Ni solid-solution in MgH2 lattice and interfacial catalysis between G-supported Ni catalysts and MgH2 matrix. Upon these effects, the dehydrogenation enthalpy and dehydrogenation activation energy of MgH2 are remarkably decreased. The finding provides a new insight into the development of high performance Mg/MgH2 based hydrogen storage composites by optimizing the doping sequence of additives.